Nitramine-containing homopolymers and co-polymers and a process for the preparation thereof

ABSTRACT

Energetic binders, and, more specifically, a class of nitramine-containing homopolymers and co-polymers characterized by favorable viscosity and glass transition temperature are prepared.

FIELD OF THE INVENTION

This invention relates generally to energetic binders, and, morespecifically, to a class of nitramine-containing homopolymers andco-polymers characterized by favorable viscosity and glass transitiontemperature.

BACKGROUND OF THE INVENTION

Certain energetic binders which are useful in propellants and explosivesformulations are known in the art. By way of illustration, a compoundcalled GAP (glycidyl azide polymer) is known to provide energy andfunction as a binder when formulated in propellants and explosives usedin various applications. However, materials such as GAP are veryexpensive, costing up to $100 per pound and are known to release gasesduring storage and/or prior to or during processing. In addition, toxicand explosive ingredients are required to produce this polymer.Therefore, alternate high energy binders that are less expensive andsafer to produce and still afford a good combination of desirablecharacteristics, such as a high impetus, a low glass transitiontemperature, and a low viscosity, would be highly desired by thepropellant and explosives community.

Various nitropolymers have been fabricated in the past for applicationin solid, smokeless propellants. For example, Aerojet General publisheda report, Report No. 1162, dated Sept. 28, 1956, entitled "Research inNitropolymers and Their Application to Solid Smokeless Propellants".This report documents various polymerization reactions useful in makingnitropolymers, including various esters of nitramino diacids. Thesepolymers, however, generally have a higher molecular weight than mightbe desired and do not possess carefully controlled, reactive, functionalend groups as would be desirable.

Hercules Incorporated investigated a specific nitramine-containingpolymer, poly(diethylene glycol-4,7-nitrazadecanedioate) designated asP-DEND. In a report entitled "High Performance Minimum SmokePropellants", Technical Report CR-RD-PR-86-4, dated May, 1986. Herculesdocuments work performed for the U.S. Army Missile Command whereinP-DEND is described as being a feasible ingredient for use in nitrateester-plasticide propellants. This report states that attempts tofabricate P-DEND by an acid catalyzed esterification reaction of4,7-dinitrazadecanedioic acid (DNDA) with diethylene glycol in a varietyof organic solvents were unsuccessful. This failure is attributed in thereport to the fact that a cyclization reaction rather than apolymerization reaction occurred. More recently, the prsent inventorshave found that P-DEND has a viscosity and a glass transitiontemperature that are higher than might be desired.

New polymer binders exhibiting excellent impetus and characterized by anadvantageous viscosity and glass transition temperature would be highlydesirable to the propellants and explosives community.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to novelnitramine-containing polymers characterized by an advantageouscombination of a low viscosity and a low glass transition temperature.The novel polymers are characterized by the following empiricalstructural formula:

    [(OOCCH.sub.2 CH.sub.2 --R--CH.sub.2 CH.sub.2 CO).sub.x (OOCCH.sub.2 CH.sub.2 --R'--CH.sub.2 CH.sub.2 CO).sub.y (OR")].sub.n

wherein R and R' are the same or different moieties selected from thegroup consisting of --N(NO₂)--, --N(NO₂)CH₂ CH₂ N(NO₂)--, and--N(NO₂)ZN(NO₂)--, wherein Z is a linear or branched-chain hydrocarbonhaving been 3 and 10 carbon atoms, with the proviso that at least one Ror R' moiety on average per molecule of said polymer must be other than--N(NO₂)CH₂ CH₂ N(NO₂)--, and wherein x represents a mole fractionhaving a value between 0 and 1, y represents a mole fraction equal to 1minus x and having a value between 0 and 1, R" is a linear or branchedchain alkylene or alkylene ether radical having between 2 and 12(preferably between 2 and 6) carbon atoms and having primary orsecondary carbon atoms at said radical's points of attachment in saidpolymer, and n has a value between 2 and 50 (preferably between 2 and20).

In another aspect, the present invention relates to a process forproducing a nitramine-containing polymer which comprises the steps ofreacting a nitramine-containing dicarboxylic acid monomer with a diolmonomer in the presence of an acid catalyst by a melt polymerizationreaction to form said nitramine-containing polymer while removingby-product water during the course of said reaction.

After the reaction has begun and particularly during the later stage ofthe reaction, it is preferred that water be removed by vacuumdistillation or as the azeotropic reaction progress in order to expediteformation of the desired nitramine-containing polymer product. Inaddition, it is preferred that the polymer product be purified in apurification step, suitably by precipitation in a solvent/non-solventmixture or by using gel permeation chromatography. If desired, thenitramine-containing polymer is end-capped with a functional moiety toimpart a desired terminal functionality to the polymer. In the absenceof such end-capping, the polymer is generally carboxyl- orhydroxyl-terminated.

DETAILED DESCRIPTION OF THE INVENTION

The polymers described in this invention are any of a variety describedby the general empirical formula given above. The polymers are preparedby reacting a nitramine-containing (i.e. nitraza-containing)dicarboxylic acid with a diol in the presence of an acid catalyst undermelt polymerization (esterification) reaction conditions (i.e. in theabsence of a solvent).

The monomers useful in the present invention include the followingdiacid (dicarboxylic) monomers: 4,7-dinitraza-1,10-decanedioic acid(DNDA); 5-methyl-4,7-dinitraza-1,10-decanedioic acid MDNDA);4-nitraza-1,7-heptanedioic acid (NHDA); 4,8-dinitraza-1,11-undecanedioicacid (DNUDA), and other diacids of similar structure. Useful diolmonomers include a wide variety of diols, such as, for example, ethyleneglycol, propylene glycol, 1,4-butane diol, 1,6-hexane diol, diethyleneglycol and various other diols of similar structure.

The homopolymers identified in Table 1 below as Polymer 5 and Polymer 8are preferred due to their relatively low glass transition temperaturewhich provides superior performance in formulated products, such aspropellants or explosives. In addition, these two polymers were found tohave relatively low viscosities which gives superior performance duringprocessing of the formulated propellant or explosive product. Otherpreferred polymers are those identified as Polymers 7, 9, 10, and 11 inTable 1 below. These co-polymers also possess relatively low viscosityand glass transition temperatures. It is preferred that the amount ofthe more rigid diacid monomer 4,7-dinitraza1,10-decanedioic acid, bekept fairly low relative to the diol monomer used to fabricate theseco-polymers, as is illustrated by the fabrication of Polymers 7 and 11.

It has been found, by virtue of the synthesis and characterization ofvarious polymer structures leading up to the present invention, thatcertain polymer structures provide products having lower glasstransition temperatures (See Table 1 below) and lower viscosities thanthose provided by prior art polymers. Specifically, Polymers 5 and 8have lower T_(g) 's and lower viscosities than the other homopolymermaterials fabricated, including the prior art polymer P-DEND (Polymer1). It is believed that these results are due to certain structuralcharacteristics of the polymer molecule. Polymer 1 has two methylenegroups between the nearest neighboring nitraza groups and exhibits ahigh glass transition temperature (0° C.) and a high viscosity. Althoughnot wishing to be bound by any particular theory, the present inventorsspeculate that this result is due to a steric hinderance or polarinteraction between the nitraza groups which inhibits rotation withinthe molecule about the molecular axis. Such interaction leads to higherglass transition temperatures and viscosities. Note that Polymer 2 has amethyl group attached to one of the two methylene groups between thenitraza groups. The fact that Polymer 2 has been found by the presentinventors to have a glass transition temperature even higher than thatof Polymer 1 supports the above-discussed steric hinderance theory.

The present inventors theorize that the larger spacing between thesterically bulky and polarized nitraza groups, such as the threemethylene groups in Polymer 8, provides a resulting polymer having alower glass transition temperature and lower viscosity. The glasstransition temperature as indicated in Table 1 for Polymer 8 is muchlower than that for Polymer 1 or Polymer 2.

Although exact viscosity measurements for these polymers has not beenmade due to sample size limitations, empirical measurements indicatePolymer 8 is less viscous than Polymer 1. This may due in part to themolecular weight differences between the two polymers, but even when avariety of higher molecular weight (as indicated by GPC) samples ofPolymer 8 were prepared, the viscosity was found to be significantlylower than that of Polymer 1.

The glass transition temperature (See Table 1 below) and the viscosityof Polymer 5 are also much lower than those of Polymers 1 and 2. As wasthe case for Polymer 8, it is believed that this, again, is due to alack of steric or polar interaction along the polymer backbone. SincePolymer 5 has an isolated nitraza group in its structure, the types ofinteractions along the molecular axis that result in hindered rotationshould not occur.

As can be seen from Table 1, various co-polymers can be prepared byusing a blend of two or more diacids. Polymers 7 and 11 were preparedusing 30 percent 4,7-dinitraza-1,10-decanedioic acid ("DNDA") which hasa slightly higher energy content on a weight basis than the diacidmonomers used for the preparation of Polymers 5 and 8, but, as mentionedabove, provides higher Tg's and viscosities for the resultingco-polymers than were obtained for the homopolymers. Fortunately, theglass transition temperatures for the resulting co-polymers preparedusing a 30 percent DNDA level are acceptable. Moreover, the DNDAprovides enhanced calculated energy content for the polymer. Polymer 6which contains 70 percent 4,7-dinitraza-1,10decanedioic acid, does showa higher Tg than Polymer 5. Thus, if a large amount of4,7-dinitraza-1,10-decanedioic acid is used as monomer, the propertiesof the binder tend to have less desirable characteristics analogous tothose of homopolymers of 4,7-dinitraza-1,10-decanedioic acid (P-DEND).

The polymers and co-polymers of the present invention combine theadvantages cited above with high calculated (by the Naval Weapons CenterPEP method) impetus in propellant formulations, a desired functionalityof very near two, primarily hydroxyl termination (if desired) of thepolymer chains, and a molecular weight which can readily be controlledto any desired value. The preferred polymer molecular weight is betweenabout 500 and about 10,000.

Note that the molecular weight of the polymers can be controlled byvarying the stoichiometry of the diol and diacid monomers. Typically,the polymers are prepared using an excess of the diol monomer relativeto the diacid, thereby providing a hydroxy-terminated polymer.Alternately, the polymer may be terminated by carboxyl groups by thesimple technique of adjusting the stoichiometric ratio of monomers suchthat the diacid (i.e. the dicarboxylic acid monomer) is present inexcess relative to the diol monomer. As another alternative, otherfunctional moieties can be used to end-cap the polymer molecules toimpart a desired terminal functionality to the polymer. For example, thehydroxy-terminated polymer can be reacted with an excess of diisocyanateto yield an isocyanate-terminated polymer. Alternately, a diacidchloride such as adipoyl chloride, phosgene, or other similar compoundscan be reacted with the hydroxy-terminated polymer to give polymersterminated with acid chloride or chloroformate groups. In similar ways,the carboxyl end groups of the carboxy-terminated polymer can bechemically modified to yield any of a variety of functional groups asterminal groups for these polymers. This flexibility in designing theend group or terminal group on the polymer molecule is important becauseit allows a great range of possibilities in terms of the curing of thesematerials with other components to fabricate the desired final product,namely the propellant or explosive product.

The reaction time useful for the process of the present invention is notnarrowly critical and can vary over a wide range. It is preferred thatthe reaction time be between about 2 and about 8 hours, more preferablybetween about 3 and about 5 hours.

Likewise, the reaction temperature is not narrowly critical and can varyover a wide range. Preferably the reaction temperature is between about60° C. and about 150° C., more preferably between about 95° C. and about125°, and most preferably between about 105° C. and about 115° C.

The process of the present invention is conducted in the presence of anacid catalyst. Suitable acid catalysts include the following: p-toluenesulfonic acid, sulfuric acid, zinc acetate, cadmium acetate, and anyother acid catalyst suitable for esterification reactions. The yield,molecular weight, polymer properties, and process variables will differdepending upon the catalyst employed.

The reaction in accordance with the present invention is preferablysuitably conducted, for the most part, at subatmospheric pressure, mostpreferably at a pressure of between about 0.001 mm of Hg and about 600mm of Hg. The subatmospheric pressure makes it possible for easy removalof the water by-product from the reaction mixture, thereby driving thepolycondensation reaction to completion as desired. Because of thevolatility of some of the monomers employed, however, subatmosphericpressure is preferably not applied during the initial stage of thereaction. Alternative or additional methods can be used to removeby-product water from the reaction mixture such as azeotropicdistillation, chemical drying, or the like.

The optional polymer purification step, if utilized, is preferablyconducted by precipitation in a mixture of a paired solvent/non-solvent.Suitable solvent/non-solvent pairs can be chosen from the followingsolvents: methylene chloride, chloroform, tetrahydrofuran, or any otherorganic solvent capable of dissolving the polymers; and the followingnon-solvents; methanol, ethanol, water, hexane, cyclohexane, benzene orany other organic medium which is not a solvent for polymers.Alternately, other purification methods can be employed such as gelpermeation chromatography.

The polymers produced in accordance with the process of the presentinvention generally have a weight average molecular weight of betweenabout 500 and about 10,000, preferably between about 1000 and about5000. The glass transition temperature of the polymer (T_(g)) isgenerally less than 0° C., preferably less than -10° C., and morepreferably less than -15° C. The viscosity of the polymer is generallyless than 50,000 centipoise, preferably less than 20,000 centipoise, andmore preferably less than 10,000 centipoise.

As used herein, the term "percent" designates weight percent and theterm "fraction" designates mole fraction unless otherwise specified.

The aforementioned technical publications are incorporated herein byreference in their entirety.

The following examples are intended to illustrate, but in no way limitthe scope of, the present invention.

EXAMPLE 1 Novel Process for Synthesizing Poly(DiethyleneGlycol-4,7-Dinitraza-1,10-Decanedioate) (Also Called "P-DEND") SeePolymer 1 of Table 1 Below

A 5 ml one-neck flask equipped with a magnetic stirring bar and anitrogen adaptor was charged with 1.00 g (4.18 mmol) of4,7-dinitraza-1,10-decanedioic acid (DNDA), 0.44 g (4.19 mmol) ofdiethylene glycol and 3 mg of p-toluene sulfonic acid. The mixture washeated to 100° C. and stirring started when the mixture melted. Themixture was heated for 5 hours and when vacuum was applied for a periodof 1.5 hours at 100° C. Then the mixture was cooled to room temperatureand dissolved in 3 ml of methylene chloride. The polymer wasprecipitated by pouring the methylene chloride solution into 40 ml ofmethanol. The methanol was decanted and the tacky polymer dried in avacuum oven at 60° C. overnight. The yield of the Polymer 1 product was0.88 g (69%) based on diacid used. The physical data is given inTable 1. Polymer 1 is a comparison composition (P-DEND) for purposes ofthe present invention; however, its preparation as described above isbelieved to be novel.

EXAMPLE 2 Synthesis of Polymer 2 Identified in Table 1

Polymer 2 was prepared by the same method as described for 1 by using1.54 g (5 mmol) of 5-methyl-4,7-dinitraza-1,10-decanedioic acid (MDNDA),0.53 g (5 mmol) of diethylene glycol and 3 mg of p-toluene sulfonicacid. The yield 1.45 g (77%) based on diacid used. The physical data isgiven in Table 1.

EXAMPLE 3 Synthesis of Polymer 3 Identified in Table 1

Polymer 3 was prepared by the same method as described for 1 by using0.27 g (0.88 mmol) of 5-methyl-4,7-dinitraza-1,10-decanedioic acid(MDNDA), 0.600 g (2.04 mmol) of 4,7-dinitraza-1,10-decanedioic acid(DNDA), 0.41 g (3.95 mmol) of diethylene glycol and 2 mg of p-toluenesulfonic acid. The yield 0.8 g (69%) based on diacids used. The physicaldata is given in Table 1.

EXAMPLE 4 Synthesis of Polymer 4 Identified in Table 1

Polymer 4 was prepared by the same method as described for 1 by using1.08 g (3.5 mmol) of 5-methyl-4,7-dinitraza-1,10-decanedioic acid(MDNDA), 0.44 g (1.5 mol) of 4,7-dinitraza-1,10-decanedioic acid (DNDA),0.5311 g (5 mmol) of diethylene glycol and 2 mg of p-toluene sulfonicacid. The yield is 1.46 g (78%) based on diacids used. The physical datais given in Table 1.

EXAMPLE 5 Synthesis of Polymer 5 Identified in Table 1

Polymer 5 was prepared by the same method as described for 1 by using1.80 g (8.73 mmol) of 4-nitraza-1,7-heptanedioic acid (NHDA), 1.04 g(9.81 mmol) of diethylene glycol and 5 mg of p-toluene sulfonic acid.The yield was 2.44 g (96%) based on diacid used by precipitating thepolymer in hexane. The physical data is given in Table 1.

EXAMPLE 6 Synthesis of Polymer 6 Identified in Table 1

Polymer 6 was prepared by the same method as 1 by using 1.47 g (5 mmol)of 4,7-dinitraza-1,10-decanedioic acid (DNDA), 0.44 g (2.13 mmol) of4-nitraza-1,7-heptanedioic acid (NHDA), 0.85 g (8.02 mmol) of diethyleneglycol and 5 mg of p-toluene sulfonic acid. The yield was 2.08 g (96%)based on diacid used. The physical data is given in Table 1.

EXAMPLE 7 Synthesis of Polymer 7 Identified in Table 1

Polymer 7 was prepared by the same method as 1 by using 0.76 g (2.57mmol) of 4,7-dinitraza-1,10-decanedioic acid (DNDA), 1.24 g (6 mmol) of4-nitraza-1,7-heptanedioic acid (NHDA), 1.02 g (9.63 mmol) of diethyleneglycol and 5 mg of p-toluene sulfonic acid. The yield was 2.18 g (95%)based on diacid used. The physical data is given in Table 1.

EXAMPLE 8 Synthesis of Polymer 8 Identified in Table 1

Polymer 8 was prepared by the same method as 1 by using 1.85 g (6 mmol)of 4,8-dinitraza-1,11-undecanedioic acid (DNUDA) 0.72 g (6.74 mmol) ofdiethylene glycol and 5 mg of p-toluenesulfonic acid. The yield was 1.92g (93%) based on diacid used. The physical data is given in Table 1.

EXAMPLE 9 Synthesis of Polymer 9 Identified in Table 1

Polymer 9 was prepared by the same method as 1 by using 1.23 g (4 mmol)of 4,8-dinitrazaundecanedioic acid (DNUDA), 0.35 g (1.71 mmol) of4-nitraza-1,7-heptanedioic acid (NHDA), 0.68 g (6.41 mmol) of diethyleneglycol and 4 mg of p-toluene sulfonic acid. The yield was 1.47 g (82%)based on diacids used. The physical data is given in Table 1.

EXAMPLE 10 Synthesis of Polymer 10 Identified in Table 1

Polymer 10 was prepared by the same method as 1 by using 0.62 g (2 mmol)of 4,8-dinitraza-1,11-undecanedioic acid (DNUDA), 0.96 g (4.67 mmol) of4-nitraza-1,7-heptanedioic acid (NHDA), 0.80 g (7.49 mmol) of diethyleneglycol and 5 mg of p-toluene sulfonic acid. The yield was 1.3 g (63%)based on diacids used. The physical data is given in Table 1.

EXAMPLE 11 Synthesis of Polymer 11 Identified in Table 1

Polymer 11 was prepared by the same method as 1 by using 1.08 g (3.5mmol) of 4,8-dinitraza-1,11-undecanedioic acid (DNUDA), 0.44 g (1.5mmol) of 4,7-dinitraza-1,10-decanedioic acid (DNDA), 0.60 g (5.62 mmol)of diethylene glycol and 5 mg of p-toluene sulfonic acid. The yield was1.60 g (95%) based on diacids used. The physical data is given in Table1.

EXAMPLE 12 Synthesis of Polymer 12 Identified in Table 1

Polymer 12 was prepared by the same method as 1 by using 1.54 g (5 mmol)of 4,8-dinitraza-1,11-undecanedioic acid (DNUDA), 0.36 g (5.88 mmol) ofethylene glycol, and 5 mg of p-toluenesulfonic acid. The yield 1.42 g(85%) based on diacids used. The physical data is given in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    POLYMER PREPARATION DATA                                                      MOLAR PERCENTS OF MONOMERS USED                                                                              PHYSICAL PROPERTIES OF THE POLYMER             Polymer*                                                                            DNDA.sup. ○a  %                                                                MDNDA.sup. ○b  %                                                               NHDA.sup. ○c  %                                                                DNUDA.sup. ○d  %                                                                MW.sup. ○e                                                                   T.sub.g.sup. ○f                                                        (°C.)                                                                         Decomposition                                                                 (°C.)              __________________________________________________________________________    1     100     --      --      --       4253  0      222.0                     2     --      100     --      --       1907  0.75   243.2                     3     70      30      --      --       3664  -6.5   --                        4     30      70      --      --       1912  --     --                        5     --      --      100     --       2511  -19.1  228.0                     6     70      --      30      --       4775  -9.5   261.4                     7     30      --      70      --       2525  -20.5  255.0                     8     --      --      --      100      2932  -22    256.0                     9     --      --      30      70       2217  -22    258.2                     10                    70      30       2026  -15    261.0                     11    30                      70       2880  -20    255.6                     12    --      --      --      100      2418  --     --                        __________________________________________________________________________    .sup. ○a 4,7-dinitraza-1,10-decanedioic acid (DNDA).                   .sup. ○b 5-methyl-4,7-dinitraza-1,10-decanedioic acid (MDNDA).         .sup. ○c 4-nitraza-1,7-heptanedioic acid (NHDA).                       .sup. ○d 4,8-dinitraza-1,11-undecanedioic acid (DNUDA).                .sup. ○e Weight average molecular weight.                              .sup. ○f Glass transition temperature of the polymer.                  *In Table 1, the various numbered polymers are more specifically              identified by the empirical structural formula as follows:                    [(OOCCH.sub.2 CH.sub.2RCH.sub.2 CH.sub.2 CO).sub.x (OOCCH.sub.2 CH.sub.2R'    H.sub.2 CH.sub.2 CO).sub.y (OR")].sub.n                                       wherein  -n had a value of between 3 and 10, and                              wherein:                                                                          R                   R'                 x  y   R"                          __________________________________________________________________________    1.  N(NO.sub.2)CH.sub.2 CH.sub.2 N(NO.sub.2)                                                          --                 1  0   CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2               ##STR1##           --                 1  0   CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          3.  N(NO.sub.2)CH.sub.2 CH.sub.2 N(NO.sub.2)                                                           ##STR2##          0.7                                                                              0.3 CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          4.  N(NO.sub.2)CH.sub.2 CH.sub.2 N(NO.sub.2)                                                           ##STR3##          0.3                                                                              0.7 CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          5.  N(NO.sub.2)         --                 1  0   CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          6.  N(NO.sub.2)CH.sub.2 CH.sub.2 N(NO.sub.2)                                                          N(NO.sub.2)        0.7                                                                              0.3 CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          7.  N(NO.sub.2)CH.sub.2 CH.sub.2 N(NO.sub.2)                                                          N(NO.sub.2)        0.3                                                                              0.7 CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          8.  N(NO.sub.2)CH.sub.2 CH.sub.2 CH.sub.2 N(NO.sub.2)                                                 --                 1  0   CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          9.  N(NO.sub.2)CH.sub.2 CH.sub.2 CH.sub.2 N(NO.sub.2)                                                 N(NO.sub.2)        0.3                                                                              0.7 CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          10. N(NO.sub.2)CH.sub.2 CH.sub.2 CH.sub.2 N(NO.sub.2)                                                 N(NO.sub.2)        0.7                                                                              0.3 CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          11. N(NO.sub.2)CH.sub.2 CH.sub.2 N(NO.sub.2)                                                          N(NO.sub.2)CH.sub.2 CH.sub.2 CH.sub.2 N(NO.sub.2)                                                0.3                                                                              0.7 CH.sub.2 CH.sub.2                                                             OCH.sub.2 CH.sub.2          12. N(NO.sub.2)OH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 N(NO.sub.2)                                                           1  0   CH.sub.2 CH.sub.2           __________________________________________________________________________

What is claimed is:
 1. A nitramine-containing polymer characterized byan advantageous combination of a low viscosity and a low glasstransition temperature and represented by the following empiricalstructural formula:

    [(OOCCH.sub.2 CH.sub.2 --R--CH.sub.2 CH.sub.2 CO).sub.x (OOCCH.sub.2 CH.sub.2 --R'--CH.sub.2 CH.sub.2 CO).sub.y (OR")].sub.n

wherein R and R' are the same or different moieties selected from thegroup consisting of --N(NO₂)--, --N(NO₂)CH₂ CH₂ N(NO₂)--, and--N(NO₂)ZN(NO₂)--, wherein Z is a linear or branched-chain hydrocarbonhaving between 3 and 10 carbon atoms, with the proviso that at least oneR or R' moiety on average per molecule of said polymer must be otherthan --N(NO₂)CH₂ CH₂ N(NO₂)--, and wherein x represents a mole fractionhaving a value between 0 and 1, y represents a mole fraction equal to 1minus x and having a value between 0 and 1, R" is a linear or branchedchain alkylene or alkylene ether radical having between 2 and 12 carbonatoms and having primary or secondary carbon atoms at said radical'spoints of attachment in said polymer, and n has a value between 2 and50, said polymer being prepared by reacting a nitramine-containingdicarboxylic acid with a diol, said nitramine-containing dicarboxylicacid being selected from the group consisting of4,7-dinitraza-1,10-decanedioic acid (DNDA);5-methyl-4,7-dinitraza-1,10-decanedioic acid (MDNDA);4-nitraza-1,7-heptanedioic acid (NHDA); 4,8-dinitraza-1,11-undecanedioicacid, and combinations thereof; and said diol being selected from thegroup consisting of ethylene glycol, propylene glycol, 1,4-butane diol,1,6-hexane diol, diethylene glycol and combinations thereof.
 2. Thepolymer of claim 1 which is terminated by primary hydroxyl groups. 3.The polymer of claim 1 wherein x is 1, y is 0, and R is N(NO₂).
 4. Thepolymer of claim 1 wherein x is 1, y is 0, and R is N(NO₂)CH₂ CH₂ CH₂N(NO₂).
 5. The polymer of claim 1 wherein x is 0.3, y is 0.7, R isN(NO₂)CH₂ CH₂ N(NO₂), and R' is N(NO₂).
 6. The polymer of claim 1wherein x is 0.3, y is 0.7, R is N(NO₂) and R' is N(NO₂)CH₂ CH₂ CH₂N(NO₂).
 7. The polymer of claim 1 wherein x is 0.7, y is 0.3, R isN(NO₂), and R' is N(NO₂)CH₂ CH₂ CH₂ N(NO₂).
 8. The polymer of claim 1wherein x is 0.3, y is 0.7, R is N(NO₂)CH₂ CH₂ N(NO₂), and R' isN(NO₂)CH₂ CH₂ CH₂ N(NO₂).
 9. The polymer of claim 1 which is terminatedby carboxyl groups.
 10. The polymer of claim 1 wherein the polymer isend-capped by reacting said polymer with a functional moiety to impart adesired terminal functionality to said polymer.
 11. A process forproducing a nitramine-containing polymer which comprises the steps ofreacting a nitramine-containing dicarboxylic acid monomer with a diolmonomer in the presence of an acid catalyst by a melt polymerizationreaction to form said nitramine-containing polymer while removingby-product water during the course of said reaction.
 12. The process ofclaim 11 wherein said by-product water is removed by distillationthereof.
 13. The process of claim 11 wherein by-product water is removedduring the course of said reaction by vacuum distillation with theproviso that a vacuum is applied only after any volatile monomerreactants have reacted.
 14. The process of claim 11 wherein saidnitramine-containing polymer is purified by precipitation using a pairedsolvent/non-solvent mixture.
 15. The process of claim 14 wherein thesolvent is selected from the group consisting of methylene chloride,chloroform, tetrahydrofuran, and mixtures thereof.
 16. The process ofclaim 14 wherein the non-solvent is selected from the group consistingof water, methanol, ethanol, hexane, cyclohexane, benzene, and mixturesthereof.
 17. The process of claim 11 which is conducted at a reactiontemperature of between about 60° C. and about 150° C.
 18. The process ofclaim 11 which is conducted at a reaction pressure of atmospheric orsubatmospheric pressure.